Adding item in front of a list

[Ben Hutchings]

In article <b7deoe$devs8$1 at ID-169208.news.dfncis.de>,
Greg Ewing (using news.cis.dfn.de) wrote:
> Alex Martelli wrote:
>> I *hate* the few places in the Nutshell in which
>> I couldn't explain a function's behavior by means of Pythonic "optional
>> arguments", but rather had to resort to brackets meaning "optional"
> 
> Maybe Python should in general allow optional arguments to
> be on the left instead of the right:
> 
>    def myrange(start = 0, stop):
>      ...
> 
> and then range() and insert() wouldn't be anomalous!

It could allow optional parameters to be defined anywhere in the list,
with the rules that:

1. Each keyword argument must correspond to a named parameter, unless
   the function accepts arbitary keyword arguments.  Keyword arguments
   are assigned to parameters first.
2. There must be at least as many non-keyword arguments (m) as there are
   unassigned required parameters (n).  Unless the function accepts
   arbitrary non-keyword arguments, there must be no more non-keyword
   arguments than there are unassigned parameters.
3. The non-keyword arguments are assigned to the first (m - n) unmatched
   optional parameters, and the n unassigned required parameters, in
   order of parameter declaration.

Then range would be range(start=0, stop, step=1).  But having existing
arguments match different parameters when you add arguments to the end
of the list could be confusing.